Atom | The smallest unit of an element that retains its chemical identity.
Cell | The basic structural and functional unit of a living organism.
Gravity | The attractive force between objects that have mass.
Friction | A force that opposes motion between touching surfaces.
Evaporation | Liquid at the surface changes into a gas.
Condensation | Water vapor cools and changes into liquid water.
Photosynthesis | Plants use light energy to turn carbon dioxide and water into sugars.
Ecosystem | Living organisms and their nonliving environment interacting together.
Food chain | A sequence showing how energy moves from one organism to another.
Habitat | The place where an organism lives and obtains what it needs.
Predator | An animal that hunts and eats other animals.
Prey | An animal that is hunted and eaten by another animal.
Vertebrate | An animal with a backbone inside its body.
Invertebrate | An animal without a backbone inside its body.
Water cycle | The continuous movement of water through the environment.
Carbon dioxide | A gas released during respiration and used by plants in photosynthesis.
Oxygen | A gas used by many organisms during cellular respiration.
Chlorophyll | The green pigment that absorbs light for photosynthesis.
Renewable energy source | An energy source naturally replenished on a human timescale.
Nonrenewable energy source | An energy source that is not replenished on a human timescale.
Conservation of energy | Energy can be transferred or transformed but cannot be created or destroyed.
Gravitational potential energy | Stored energy due to an object's position in a gravitational field.
Electromagnetic radiation | Energy carried by waves that can travel through empty space.
Thermal energy transfer | Energy moving from a warmer object to a cooler object.
Chemical reaction | A process that changes substances into different substances.
Electrical conductor | A material that allows electric charge to move through it easily.
Electrical insulator | A material that strongly resists the movement of electric charge.
Independent variable | The variable deliberately changed in a controlled experiment.
Dependent variable | The variable measured to observe the effect of a change.
Controlled experiment | A test in which relevant conditions are kept the same except one variable.
Natural selection | A process in which inherited traits affect survival and reproduction.
Cellular respiration | Cells release usable energy by breaking down food molecules.
Decomposition | The breakdown of dead organisms and organic material.
Adaptation | An inherited feature that helps an organism survive or reproduce.
Surface area to volume ratio | A comparison of the outside surface of an object with its internal volume.